There’s no shortage of reasons that many Americans don’t get enough sleep: stress, obesity, late-night shifts on the job, to name just a few. Now new research suggests another factor to consider as well — their race or ethnicity.

In two presentations at the annual meeting of the Associated Professional Sleep Societies in Boston, scientists report that the amount and quality of sleep people get each night vary across racial and ethnic lines. In one study, researchers found that blacks and Asians don’t sleep as much as whites do, while another study showed that foreign-born Americans are less likely to report having sleep problems than those born in the U.S.

A better understanding of these discrepancies could help researchers improve the sleep habits of particular groups — a potential public-health boon, considering that inadequate sleep is increasingly associated with greater risks of chronic conditions like heart disease, diabetes, obesity and certain cancers.

For the first study, led by Mercedes Carnethon, an associate professor of preventive medicine at Northwestern University, researchers randomly selected 439 Chicago-area adults from the phone book to participate. The volunteers, aged 35 to 64, were of white, black, Hispanic or Asian descent. Researchers screened the participants for sleep disorders like sleep apnea, and then asked them to wear a wrist monitor that detected their movements and determined how much time they spent sleeping over a period of seven days. The participants also self-reported the amount and quality of sleep they got each night.

Overall, the researchers found, blacks, Hispanics and Asians slept less than whites. Blacks got 6.8 hours of sleep a night on average, compared with 6.9 hours for Hispanics and Asians, and 7.4 hours a night for whites. The differences in sleep times persisted even after the researchers adjusted for other factors known to interfere with sleep, such as weight, diabetes status, high blood pressure and other heart disease risk factors. The study authors also accounted for socioeconomic factors like low education and low income, both of which can increase stress and disrupt sleep.

Interestingly, despite the fact that every racial group got less sleep than whites, only blacks reported suffering poor sleep quality and only Asians reported significant levels of daytime sleepiness. The latter finding was particularly surprising, since Asians tended to have lower body mass indexes and higher or equal education levels as whites, but still showed shorter and poorer sleep. “It’s one of our more compelling and interesting findings, and one we intend to explore in depth further,” says Carnethon, who notes that there’s very little data on the sleep habits of Asians.

The authors surmise that the majority of the differences in sleep patterns between races can be chalked up to environmental or even geographical factors — rather than genes or physical characteristics like variations in facial structure that could interfere with breathing and sleep. For example, Carnethon notes that Chicago is a relatively segregated city, and blacks and Hispanics tend to live in areas with higher pollution, more mass transit noise and higher crimes rates than predominantly white neighborhoods, which can lead to stress and disturbed sleeping. “I think social factors are more likely to account for the race and ethnic differences we observed,” she says.

In the other paper, presented by Dr. Abhishek Pandey of SUNY Downstate Medical Center, scientists compared nightly sleep duration between foreign-born Americans and those who were born in the U.S. Based on phone survey data collected on 434,849 participants in the National Health Interview Survey in 2004-10, the researchers found that U.S.-born residents were more likely to report longer sleep — more than eight hours a night on average — while African-born Americans reported the least, less than six hours a night. Indian-born Americans fell in between, getting six to eight hours of sleep on average per night. The differences held even after the researchers adjusted for factors that can affect sleep duration, such as weight, age, and health risk behaviors such as smoking and drinking alcohol.

But despite their shorter sleep, foreign-born Americans were 20% less likely to report getting insufficient sleep than their native-born counterparts. While the study wasn’t designed to determine why a person’s country of birth might have such a strong effect on their sleep patterns, Pandey says that cultural beliefs and attitudes about sleep may influence how people view the importance of getting enough nightly slumber. In a previous study of Afro-Caribbean men in Brooklyn, for example, Pandey says that about 60% reported short sleep, but weren’t aware of the health effects of sleep deprivation.

Taken together, the findings suggest that when it comes to sleep, a individual’s racial or ethnic heritage may not only help explain his or her sleep patterns, but also encourage certain groups to sleep longer by addressing culturally based misperceptions about healthy sleep. In the U.S., racial ancestry has a lot to do with how we live our lives — whether we’re awake or asleep.